Ignition system having a controlled rectifier



Oct. 19, 1965 w, WORRELL 3,213,320

IGNITION SYSTEM HAVING A CONTROLLED RECTIFIER Filed April 5, 1962 /2 GEKW H/S ATTORNEY I INVENTOR, 6

United States Patent Q 3,213,320 IGNITION SYSTEM HAVING A CONTROLLED RECTIFHER William I). Worrell, Anderson, Ind., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Fiied Apr. 5, 1962, Ser. No. 185,284 6 Claims. (Cl. 315209) This invention relates to ignition systems for internal combustion engines and more particularly to an ignition system wherein a controlled rectifier controls current flow through the primary winding of an ignition coil.

In present day internal combustion engine ignition systems, it is common practice to control the current fiow through the primary winding of an ignition coil by a pair of breaker contacts that are opened and closed in synchronism with movement of the engine. Although this system has for the most part been satisfactory, it has disadvantages in that the breaker contacts must open a circuit that is highly inductive with a consequent burning and pitting of the breaker contacts. The fact that the breaker contacts must open and close many thousands of times over a given trip also plays a part in their deterioration especially in view of the high current that they must make and break.

In contrast to the above described conventional ignition system, it is an object of this invention to provide an ignition system wherein the current flow through the breaker contacts is greatly reduced as compared to a conventional ignition system.

A more specific object of this invention is to provide an ignition system wherein a controlled rectifier controls cur rent flow through the primary winding of an ignition coil and wherein the gate electrode of the controlled rectifier has its voltage changed by the opening and closing of a pair of breaker contacts operated in synchronism with the engine.

Another object of this invention is to provide an ignition system wherein a controlled rectifier controls current flow through the primary winding of an ignition coil and wherein the gate voltage of the controlled rectifier is varied by the opening and closing of a pair of breaker contacts, the system further including an energy storing circuit element which sharply turns off the controlled rectifier and then permits it to turn back on when the breaker contacts open.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein preferred embodiments of the present invention are clearly shown.

In the drawing:

FIGURE 1 is a schematic circuit diagram of an ignition system made in accordance with this invention.

FIGURE 2 is a schematic circuit diagram of a modified ignition system made in accordance with this invention.

Referring now to the drawings and more particularly to FIGURE 1, the reference numeral 10 designates an internal combustion engine which is supplied with spark firing energy from the ignition system of this invention. The engine 10 is mechanically coupled to a distributor which includes the breaker cam 12. The cam 12 operates a breaker lever 14 carrying an electrical contact 16 which cooperates with the fixed contact 18. When the engine is running or being cranked, the cam 12 causes the contacts 16 and 18 to become engaged and disengaged in a manner well-known to those skilled in the art. The fixed contact 18 is grounded as shown whereas the contact 16 is con nected with the breaker lever 14 and with a lead wire 20.

The power supply for the ignition system shown in FIGURE 1 takes the form of a battery 22. The battery 22 on a motor vehicle will of course be connected with a 3,213,320 Patented Oct. 19, 1955 suitable generator and under certain conditions, the generator will supply the ignition power. One side of the battery is connected directly to ground whereas the opposite side of the battery is connected with an ignition switch 24. The ignition switch 24 is connected with a lead wire 26 and this lead wire is connected with junctions 28 and 30.

An ignition coil generally designated by reference numeral 32 is provided which has a primary winding 34 and a secondary winding 36. The secondary winding 36 is shown connected directly with a spark plug 38 but it will be understood by those skilled in the art that electrical energy coming from the secondary winding 36 can be distributed to a plurality of spark plug by a suitable distributor. It is seen that one side of the secondary winding 36 is connected directly to ground as is one side of the spark plug 38.

The current flow through the primary winding 34 of ignition coil 32 is turned on and ofi by a controlled rectifier 40 having an anode 42, a cathode 44 and a gate electrode 46. The controlled rectifier 40 is a semiconductor device which will permit current flow between the anode 42 and the cathode 44 whenever the gate electrode 46 is positive with respect to the cathode 44. If the gate electrode 46 is made sufliciently negative with respect to cathode 44, the controlled rectifier turns off and does not permit current flow between its anode and cathode. This controlled rectifier must be of the type that can be turned ofi" by a variation-in voltage applied to the gate electrode 46.

The anode 42 of controlled rectifier 40 is connected with junction whereas the cathode 44 of controlled rectifier is connected with the junction 48. A resistor connects the junction 48 and the primary winding 34 of the ignition coil.

The gate electrode 46 of the controlled rectifier 40 is connected with a junction 52 via the resistor 54. The junction 52 is connected with junction 28 through resistor 56 and is connected to ground through resistor 58. The junction 52 is connected with lead wire 20 and thus is connected with one of the breaker contacts 16. A capacitor is connected across the anode and cathode of the controlled rectifier.

In order to start the engine 10 with the ignition system of FIGURE 1, the ignition switch 24 is closed and the engine cranked by a suitable cranking motor not shown. Cranking of the engine 10 will cause the breaker contacts 16 and 18 to open 0nd close in the same manner as when the engine is running.

When the breaker contacts 16 and 18 are open, the controlled rectifier 40 is turned on to permit current flow from anode to cathode and through the resistor 50 to the primary winding 34. With the breaker contacts open, a voltage is developed at junction 52 which depends upon the resistance of the voltage divider resistors 56 and 58. The resistance values of resistors 56 and 58 are so chosen that with the contacts 16 and 18 in an open position, the potential at junction 52 is higher or more positive than the potential at junction 48. This means that the potential of the gate electrode 46 is positive with respect to the potential of the cathode 44 and the controlled rectifier 40 is therefore turned on to permit a high current flow through the primary winding 34.

When the breaker contacts 16 and 18 close, the junction 52 will have its potential lowered toward ground potential. The potential of point 48 will thus be higher than the potential of junction 52 and as a result, the gate electrode 46 of the controlled rectifier 40 is driven negative with respect to the potential of the cathode 44. This will cause the controlled rectifier 40 to turn off between its anode and cathode and will therefore interrupt the current flow through the primary winding 34.

3 This will result in a large voltage being induced in the secondary winding 36 which then is used to fire the spark plug 38.

The resistor 54 is included in the system of FIGURE 1 to limit the gate current of the controlled rectifier to a desired value. The resistor 50 limits the current through the primary winding 34 to a desired value. The purpose of capacitor 60 is to protect the controlled rectifier 40 from transients produced by ignition coil 32.

Referring now more particularly to FIGURE 2, a modified ignition system is illustrated. In the system of FIGURE 2, the firing of the spark plug occurs upon an opening of the breaker contacts rather than upon closing of the breaker contacts as in FIGURE 1. The FIGURE 2 system also includes an energy storing circuit element which is used to turn off the controlled rectifier when the breaker contacts open. In FIGURE 2, the same reference numerals have been used as in FIGURE 1 to identify equivalent parts in the two systems.

In the system of FIGURE 2, it is seen that the controlled rectifier 40 is connected in series with a resistor 62 and in series with the primary winding 34 of the ignition coil. The anode 42 of the controlled rectifier is connected with resistor 62 and this resistor is connected with the junction 66 through lead wire 64. One side of a diode 68 is connected with junction 66, the opposite side of the diode being connected with a resistor 70. The resistor 70 is connected with a junction 72 which in turn is connected with the gate electrode 46 via resistor 74. An inductive choke 76 is connected between junctions 72 and 78. A capacitor 80 is connected between junction 78 and ground. The breaker contact 16 is connected with junction 78 via the lead wire 82.

When the ignition switch 24 of FIGURE 2 is closed and the breaker contacts 16 and 18 are separated, the controlled rectifier 40 is biased to a state of full conduction. The controlled rectifier 40 is turned on by current flow through diode 68, resistor 70, resistor 74, the gate to cathode junction of controlled rectifier 40 and primary winding 34. With controlled rectifier 40 turned on, current will fiow through primary winding 34 and flux will be built up in the ignition coil.

When breaker contacts 16 and 18 close, the battery 22 supplies current to the series circuit that includes the diode 68, resistor 70, choke coil 76, and then through the closed breaker contacts 16 and 18 to ground. Thiswill cause the junction 72 to be at a slightly lower potential than junction 84, but this difierence in potential is not sufiicient to turn off the controlled rectifier 40. It can be seen that the closing of the breaker contacts 16 and 18 has not altered the current flow through the primary winding 34 and this current thus continues to flow.

When the breaker contacts 16 and 18 open, the energy stored in the choke coil 76 will cause a current to flow through the capacitor 80, and the potential of junction 72 will become negative with respect to ground by the amount of voltage induced in the choke coil 76. The values of resistor 70, choke coil 76 and capacitor 80 are also chosen so that it will be possible to turn the controlled rectifier 40 completely otf during the time that junction 72 is at a lower potential than junction 84.

When the controlled rectifier 40 is turned off between anode 42 and cathode 44, the current How to primary winding 34 is interrupted and a high voltage is induced in the secondary winding 36 of -the ignition coil. This energy is used to fire the spark plug 38. The capacitor 60 protects the controlled rectifier 40 from transients induced in the ignition coil 32.

When the controlled rectifier 40 has been turned completely 01f due to release of energy from the choke coil 76, the energy of the choke coil will have been dissipate d and the potential at junction 72 Will be higher than the potential at junction 84 assuming that the breaker contacts 16 and 18 have not yet closed. When junction 72 becomes positive with respect to junction 84, the controlled rectifier 49 is once more turned on to permit current flow through the primary winding 34 and to permit flux to be built up in the ignition coil 32. It is to be observed that when the breaker contacts 16 and 18 open, the release of energy from the choke coil 76 turns off the controlled rectifier 40 and this controlled rectifier is only turned off for the time that it takes for the energy from the choke coil to be dissipated. This energy can be entirely dissipated before the breaker contacts 16 and 18 reclose but the controlled rectifier is turned back on before this time as soon as the energy of the choke coil is dissipated. With the arrangement of FIGURE 2, the amount of time that the controlled rectifier is conducting is maintained at a maximum and this is important in the ignition system in order that sufiicient flux will be generated in the ignition coil 32 to cause a high voltage to be induced in the secondary winding 36 when spark plug firing is required.

The resistor 74 in FIGURE 2 performs the same func tion as resistor 54 in FIGURE 1. The resistor 62 can be moved from its position shown in FIGURE 2 to a position between junction 84 and primary winding without substantial change in operating characteristics.

While the embodiments of the present invention as herein disclosed, constitute a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. An ignition system for an internal combustion engine comprising, a source of direct current, an ignition coil having a primary winding and a secondary winding, a first resistor, a controlled rectifier having anode, cathode and gate electrodes, a first circuit connected across said source of direct current including in a series connection the primary winding of said ignition coil, the anode-cathode circuit of said controlled rectifier and said first resistor, a second circuit connected across said source of direct current in parallel with said first circuit comprising a voltage divider network having a junction, said second circuit being continuously conductive when said ignition system is energized, a second resistor, said second resistor being connected between said junction on said voltage divider network and the gate of said controlled rectifier, breaker contacts opened and closed in synchronization with operation of said engine, and means connecting said breaker contacts between said junction on said voltage divider network and one side of said source of direct current.

2. An ignition system for an internal combustion engine comprising, an ignition coil having a primary winding and a secondary winding, a source of direct current, a controlled rectifier having anode, cathode and gate electrodes, breaker contacts opened and closed in synchronism with operation of said engine, a first circuit connected across said source of direct current including in a series connection the anode-cathode circuit of said controlled rectifier and the primary winding of said ignition coil, a second circuit connected across said source of direct current including in a series connection a diode, an inductance and a capacitor, said diode and inductance both being connected to a first junction on said second circuit with said capacitor and inductance being connected to a second junction on said second circuit, means connecting the gate of said controlled rectifier with said first junction, and means connecting said breaker contacts between one side of said source of direct current and said second junction.

3. An ignition system for an internal combustion engine comprising, an ignition coil having a primary winding and a secondary winding, a source of direct current, a controlled rectifier having anode, cathode and gate electrodes, breaker contacts opened and closed in synchronism with operation of said engine, means connecting the anode and cathode electrodes of said controlled rectifier and said primary winding of said ignition coil in series and across said source of direct current, a circuit connected across said source of direct current including in a series connection, a diode, an inductance and a capacitor, means connecting said breaker contacts between one side of said source of direct current and one side of said inductance whereby current flows through said inductance when said breaker contacts are closed, and means connecting said gate electrode of said controlled rectifier to an opposite side of said inductance.

4. An ignition system for an internal combustion engine comprising, a source of direct current, an ignition coil having a primary winding and a secondary winding, a three terminal semiconductor switch having a gate, an anode and a cathode, a current limiting resistor, means connecting the anode-cathode circuit of said semiconductor switch, said primary winding of said ignition coil and said current limiting resistor in series and across said source of direct current, a voltage divider comprised of at least two elements having resistance and having a common junction, said voltage divider being connected across said source of direct current, a resistor connected between said common junction and the gate of said semiconductor switch, breaker contacts opened and closed in synchronism with operation of said engine, and means connecting said breaker contacts between said common junction on said voltage divider and one side of said source of direct current.

5. An ignition system for an internal combustion engine comprising, a source of direct current, a three terminal semiconductor switch having a gate, an anode and a cathode, an ignition coil having a primary winding and a secondary winding, means connecting the anode-cathode circuit of said semiconductor switch and said primary winding of said ignition coil in series and across said source of direct current, breaker contacts opened and closed in synchronism with operation of said engine, a biasing circuit including a reference potential point connected across said source of direct current and continuously conductive when said system is energized, means connecting said reference potential point with the gate of said semiconductor switch, means connecting said biasing circuit with said source of direct current in such a manner that said reference potential point has a potential which is effective to normally bias said semiconductor switch to a state of conduction, means connecting said breaker contacts between said source of direct current and said reference potential point whereby the potential of said reference potential point varies as said breaker points open and close, and a capacitor connecting the anode and cathode electrodes of said semiconductor switch.

6. An ignition system for an internal combustion engine comprising, a source of direct current, a semiconductor switch having a gate, cathode and anode, an ignition coil having a primary winding and a secondary winding, means connecting the anode-cathode circuit of said semiconductor switch in series with the primary winding of said ignition coil and across said source of direct current, breaker contacts opened and closed in synchronism with operation of said engine, a circuit connected with the gate of said semiconductor switch and with said breaker contacts and source of direct current, said circuit being continuously conductive when said system is energized, said circuit applying a bias to said semiconductor switch from said source of direct current to cause said semiconductor switch to be conductive in its anode-cathode circuit in one position of said breaker contacts, said circuit biasing said semiconductor switch to a nonconductive condition in its anode-cathode circuit in another position of said breaker contacts, and a capacitor connected across the anode and cathode electrodes of said semiconductor switch.

References Cited by the Examiner UNITED STATES PATENTS 2,769,021 10/56 Crosby 315-209 3,046,447 7/62 Kirk et a1. 315-209 DAVID J. GALVIN, Primary Examiner.

ARTHUR GAUSS, Examiner. 

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE COMPRISING, A SOURCE OF DIRECT CURRENT, AN IGNITION COIL HAVING A PRIMARY WINDING AND A SECONDARY WINDING, A FIRST RESISTOR, A CONTROLLED RECTIFIER HAVING ANODE, CATHODE AND GATE ELECTRODES, A FIRST CIRCUIT CONNECTED ACROSS SAID SOURCE OF DIRECT CURRENT INCLUDING IN A SERIES CONNECTION THE PRIMARY WINDING OF SAID IGNITION COIL, THE ANODE-CATHODE CIRCUIT OF SAID CONTROLLED RECTIFIER AND SAID FIRST RESISTOR, A SECOND CIRCUIT CONNECTED ACROSS SAID SOURCE OF DIRECT CURRENT IN PARALLEL WITH SAID FIRST CIRCUIT COMPRISING A VOLTAGE DIVIDER NETWORK HAVING A JUNCTION, SAID SECOND CIRCUIT BEING CONTINUOUSLY CONDUCTIVE WHEN SAID IGNITION SYSTEM IS ENERGIZED, A SECOND RESISTOR, SAID SECOND RESISTOR BEING CONNECTED BETWEEN SAID JUNCTION ON SAID VOLTAGE DIVIDER NETWORK AND THE GATE OF SAID CONTROLLED RECTIFIER, BREAKER CONTACTS OPENED AND CLOSED IN SNCHRONIZATION WITH OPERATION OF SAID ENGINE, AND MEANS CONNECTING SAID BREAKER CONTACTS BETWEEN SAID JUNCTION ON SAID VOLTAGE DIVIDER NETWORK AND ONE SIDE OF SAID SOURCE OF DIRECT CURRENT. 